Poly (alkylene terephthalate) resins such as poly (butylene terephthalate) (PBT), poly (ethylene terephthalate) (PET), etc. and polyamide resins such as nylon 6, nylon 66, etc. are inadequate in impact strength and, therefore, many attempts have been made to improve the impact strength.
On the other hand, polycarbonate resin inherently has high impact strength, but because of the remarkable dependency of its impact strength on molded thickness and the high melt viscosity it shows, it has the disadvantage of poor moldability.
A number of impact modifiers have been proposed for incorporation by melt-blending in such resins to improve this quality. Among them, the core-shell polymer consisting of a rubbery core and a glassy shell is characterized by the advantage that because its state of dispersion in the matrix resin is not appreciably influenced by melt-blending conditions, the reproducibility of uniform dispersion can be easily assured.
On the other hand, this core-shell polymer has the disadvantage that because of the small diameter of dispersed particles, the melt viscosity of the resin composition tends to be high.
As a core-shell polymer for improving the impact strength of poly (alkylene terephthalate) resin, a multi-phase polymer containing epoxy groups in the outermost shell phase has been proposed in Japanese laid-open Patent, Application No. 74652/1977 but this polymer is not very practically useful because the impact strength-improving effect for poly (alkylene terephthalate) resin is almost negligible and the melt viscosity of the blend is also markedly increased.
Japanese laid-open Patent Application No. 150466/1977 proposes a poly (alkylene terephthalate) resin composition modified with a core-shell polymer containing no epoxy group in the shell phase, and actually some species of the composition show high notched Izod impact strength (1/8 inch thick). However, even those compositions showing high impact strength seemingly have high melt viscosities.
As a core-shell polymer for improving the impact strength of polyamide resin, Japanese laid-open Patent Application No. 6284/1972 proposes a polyamide resin composition modified with a core-shell polymer containing carboxyl groups in the shell phase, and actually some species of the composition have high notched Izod impact strength (1/8 inch thick). However, while giving high impact strength, these compositions show markedly increased melt viscosities, thus being of little practical utility.
Core-shell polymers for improving the impact strength of polycarbonate resin have also been described in more than several publications including Japanese laid-open Patent Application No. 34153/1982,but there is not known a core-shell polymer that is used also for the purpose of improving the moldability.
Although the addition of such impact modifiers to engineering plastics such as polycarbonate resin, poly (alkylene terephthalate) resin, polyamide resin, etc. may result in improved impact strength, the practice inevitably causes increases in melt viscosity. To overcome this disadvantage, many attempts have been made, for example, blending a still another component.
Japanese Patent Publication No. 16976/1987 is an example of such endeavor but even this technique is not free from disadvantages in the aspect of product appearance, such as surface delamination, loss of surface gloss and so on.
In U.S. Pat. No. 4,684,696 it is disclosed that thermoplastic compositions comprised of poly (phenylene oxide) resin with or without a poly (alkenyl aromatic) resin such as polystyrene can be impact modified with a modifying agent having a core-shell structure comprised of an interpenetrating, crosslinked acrylate core and a crosslinked styrenic shell.
But this agent is not enough to improve the impact strength of the resin, and the moldability of the resin is still not improved enough.